The invention relates generally to inspection systems and particularly to pipeline inspection systems that use ultrasound data for detecting and sizing cracks and notches in pipelines.
Pipelines that allow a large amount of material to be transported from one place to another are widely used in a variety of industries. A variety of fluids such as oil and/or gas are transported cheaply and efficiently using pipelines. Particulate matter, and other small solids suspended in fluids may also be transported through pipelines. Underground and underwater (deep sea) pipelines typically carry enormous quantities of oil and gas products that are important to energy-related industries, often under extreme conditions such as high pressure, high (or low) temperature and high flow rate.
Flaws in constituent pipes may cause pipeline integrity degradation as the pipeline infrastructure ages. Corrosion or other pipeline defects can be caused by small spots of weakness, subsidence of the soil, local construction projects, seismic activity, weather, wear and tear caused by normal use, and the like. Accordingly, potential defects and anomalies can appear on the surface of the pipeline in the form of corrosion, mechanical damage, fatigue cracks, stress corrosion cracks, hydrogen-induced cracks, or distortion because of dents or wrinkles.
Maintaining and protecting existing pipeline networks is proving to be a challenge. Current state-of-art inline inspection systems use Pipeline Inspection Gages (PIG). PIGs move through a section of pipeline to acquire data from multiple sensors. A typical single run for the PIG may be more than 100 km long. The process of analyzing data obtained from the PIG and making practical use of the analysis is often burdensome. There are a variety of PIGs, common ones are the magnetic flux leakage PIGs used for corrosion detection and ultrasound PIGs used for crack detection. Current data analysis methods require on an average, about 200 man-days using ultrasound crack detection techniques to analyze and evaluate data from a 100 km long pipeline section.
Accurate sizing of the flaws (for example, cracks and the like) plays an important role in assessing the impact and severity of pipeline defects. Without accurate information regarding flaw size, it may be difficult to rate the quality of the pipeline or perform any remaining life estimation studies for such objects. Manual crack sizing leads to subjectivity and operator dependence, which in turn, might lead to inconsistent sizing estimates.
Ultrasonic non-destructive evaluation (NDE) methods for estimation of crack sizes in PIG based pipeline inspection include echo amplitude drop, and use of a distance-amplitude-correction curve. Most of these techniques involve assessment of reflection amplitude and acoustic shadow information by manual means. The use of amplitude data alone may not be reliable when trying to identify cracks or crack-like flaws, since the amplitude of the reflected sound signal depends on shape, size, type, orientation and position of the crack or crack-like flaw.
Therefore, there is a need for an improved technique for accurately estimating depth of cracks in pipelines and similar objects to facilitate effective repair and maintenance follow-up action.